Noninvasive Characterization of Electrical Power Distribution Systems

ABSTRACT

Embodiments of methods and apparatuses for characterizing an electrical power distribution system are disclosed. One method includes applying at least one test signal to at least one test point of the system, measuring a plurality of response signals at a plurality of test points, wherein the plurality of response signals are generated in response to the at least one test signal, and characterizing the system based on the plurality of response signals. One system includes a plurality of test/response units attached to a plurality of test points, the units configured to generate test signals and/or measure response signals at the test points. At least one controller coordinates application of the test signals and characterizes the electrical network based on the response signals. A communications link allows the test/response units to communicate with the at least one controller.

FIELD OF THE DESCRIBED EMBODIMENTS

The described embodiments relate generally to electrical system testing.More specifically, the described embodiments relate to methods andapparatuses for noninvasive characterization of electrical powerdistribution systems.

BACKGROUND

An electrical power distribution system or premises wiring of a buildingor structure whose wiring is generally inaccessible for visualinspection and for which only limited blueprint information may beavailable can be very difficult to characterize. The system is normallyused to distribute power from a centralized feed through a distributionpanel and branch circuits to various locations within the structure thatrequire a source of electricity. Such locations might include dedicatedcircuits for motors, ventilation, heating, cooling, lighting,safety-systems, alarms, or general purpose outlets. Electrical systemsusually comprise voltage sources, often connected through a servicepanel, and protected against overload by circuit breakers and fuses,distributed along branch circuits by a variety of wiring and junctionboxes, conduits, and raceways. Such wiring and boxes are often containedwithin the structure within walls, floors, or ceilings of buildings,hidden from view and difficult to access without intrusive andpotentially destructive methods.

There are a variety of voltages, currents, and multi-phase circuitspossible for common industrial, commercial, and residential powerdistribution systems. Each such circuit may be divided and furthersubdivided in the form of branch circuits that travel throughout acommercial building or dwelling. Characterizing these branch circuits iskey for determining whether the electrical system is functional andsafe.

As buildings age, the condition of the wiring deteriorates because ofnormal aging, infiltration of elements, action by vermin, sub-standardmodifications that do not meet current electrical codes, or abuse oroverloading, or incorrect installation. It would be desirable tocharacterize the electrical system condition without invasive ordestructive tests, and without endangering the personnel making suchtests. Furthermore, such characterization should not contribute to anydeterioration of the condition of the system.

There is a need to be able to easily characterize an electrical powerdistribution system or premises wiring of a building or structure whosewiring is generally inaccessible for visual inspection and for whichonly limited blueprint information may be available.

SUMMARY OF THE DESCRIBED EMBODIMENTS

An embodiment includes a method of characterizing an electrical powerdistribution system. The method includes applying at least one testsignal to at least one test point of the system, measuring a pluralityof response signals at a plurality of test points, wherein the pluralityof response signals are generated in response to the at least one testsignal, and characterizing the system based on the plurality of responsesignals.

Another embodiment includes a method of characterizing an electricalpower distribution system. The method includes applying a plurality oftest signals to a plurality of test points of the system, measuring aresponse signal at one or more test points, wherein the response signalsare generated in response to the plurality of test signals, andcharacterizing the system based on the at least one response signal.

Another embodiment includes a system for characterizing an electricalpower distribution system. The system includes a plurality oftest/response units (T/R units) attached to a plurality of test points,the units configured to generate test signals and/or measure responsesignals at the test points. At least one controller coordinatesapplication of test signals and characterizes the electrical networkbased on response signals. A communications link allows the T/R units tocommunicate with the at least one controller.

Another embodiment includes a T/R unit that is connectable to anelectrical power distribution system through a test point. The unit isoperative to apply at least one test signal to the test point, measureat least one response signal at the test point, wherein the responsesignal is generated in response to the test signal. Further, the unit isoperative to receive instructions on application of the test signalfrom, or to transmit results of the at least one measured responsesignal to another T/R unit or coordinating controller.

Another embodiment includes a T/R unit that is connectable to anelectrical power distribution system through a test point. The unit isoperative to apply at least one test signal to the test point, measureat least one response signal at the test point, wherein the responsesignal is generated in response to a test signal applied at another testpoint of the electrical power distribution system. Further, the unit isoperative to receive instructions on application of the test signalfrom, or to transmit the results of its measured response signal to,another T/R unit or coordinating controller.

Other aspects and advantages of the described embodiments will becomeapparent from the following detailed description, taken in conjunctionwith the accompanying drawings, illustrating by way of example theprinciples of the described embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of an electrical distribution system, andmultiple test/response units for testing/characterizing the electricaldistribution system.

FIGS. 2A, 2B show exemplary configurations of electrical distributionsystems that can be characterized using the described embodiments.

FIG. 3 is a flow chart that includes steps of an example of a method ofcharacterizing an electrical power distribution system.

FIG. 4 shows an example of a test/response unit.

FIG. 5 shows an example of multiple test/response units and a centralcontroller for characterizing an electrical distribution system.

FIG. 6 is a flow chart that includes steps of another example of amethod of characterizing an electrical power distribution system.

DETAILED DESCRIPTION OF INVENTION

The described embodiments provide non-invasive characterization ofelectrical power distribution systems. The described embodiments areoperable, for example, for characterizing premises wiring of a buildingor structure wherein the wiring is inaccessible for visual inspection,and for which only limited blueprint information may be available.

The embodiments for characterizing and testing of electrical powerdistribution systems are simple and economical that they can be done asdesired or deemed necessary. For example, if it is noticed by theinhabitants of the structure that there are circuits that areinoperable, excessively hot, sparking or arcing, or exposed, then suchcharacterization and tests can be used to help determine the cause. Asanother example, during the buying or selling of a structure, or otherexchange of ownership, the new owners or inhabitants might want suchtesting as a clause of the transaction.

There are known methods for testing individual electrical circuits. Suchmethods include testing probes that measure voltage at particularoutlets or other test points to ensure that wiring to that outlet isintact and proper. Such methods are generally confined to measuring theresponse at the test point to which the test signal is applied. Theembodiments described herein differ in many aspects including applyingthe test signal at one or more test points and measuring the response ata plurality of test points. Furthermore, the measurements at theplurality of test points can be processed analytically to deduceindividual circuit characteristics that cannot be deduced by measuringat individual test points alone.

FIG. 1 shows an example of an electrical distribution system 100, andmultiple test/response (T/R) units 110, 120, 130 fortesting/characterizing the electrical distribution system. As shown, theT/R units 110, 120, 130 are electrically connected to the electricaldistribution system 100 at various points (to be referred to as “testpoints”) or locations of the electrical distribution system 100.Additionally, communication links 190 are established between themultiple T/R units 110, 120, 130 allowing the multiple T/R units 110,120, 130 to communicate information about test signals applied to thetest points, and information about response signals measured at the testpoints.

As will be described, the communication links 190 between the multipleT/R units 110, 120, 130 allow for coordinated application of testsignals at one or more test points, and coordinated measurements of theresponses at one or more test points. This coordination allows for morecomplete characterization of electrical distribution systems thanavailable by single test point testing and characterization. For anembodiment, each of the test points includes at least one electricalcontact or accessible wire around which may be placed a current-probe. Acurrent-probe allows current measurements to be made without breakingthe insulation of a wire.

As will be described, a test point can include multiple electricalconductors. Further, test signals can be applied between pairs ofelectrical contacts at a test point. A test point generally means anylocation that is accessible to service personnel and connected to theelectrical system of the structure. Such test points may includestandard electrical outlets with receptacles normally used to connectappliances, or devices and switches used for control or lighting, orlighting outlets, or connection points at or within panel boxes. Suchpoints are normally found mounted on or partially within a wall, ceilingor floor. These test points are particularly suited for makingmeasurements that allow the condition of an electrical system to beascertained.

For an embodiment, characterizing the electrical power distributionsystem based on the plurality of response signals includes deducingelectrical properties of the individual branches of the electrical powerdistribution system. For another embodiment, characterizing theelectrical power distribution system based on the plurality of responsesignals includes locating at least one fault within the system.Embodiments include observing response-signals for time-variations toindicate time-varying effects.

For the purposes of description here, the term “characterization”includes determining the electrical properties of the individual circuitconductors within branch circuits of the electrical power distributionsystem. Such properties include resistances of conductors and junctions.Characteristics of a conductor in good condition include low resistance.For example, 14AWG copper wire has a normal resistance at roomtemperature of 0.0025 ohms/foot. Any characterization of resistance morethan this amount, might indicate a problem within the wire, or at ajunction in which the wire is joined to other wires. Other forms ofcharacterizations of an electrical distribution system includedetermining the number of branch circuits, the number of outlets on agiven branch circuit, identifying which outlets are connected to whichbranch circuit, and the detection of branch circuits that haveground-fault or arc-fault protection. The number of outlets, and use ofground-fault protection is generally governed by local electrical codes.

One embodiment of a “blueprint” of the electrical distribution systemincludes associating the branch outlets and branch loads with the branchcircuits. Such an embodiment allows the wiring diagram of the dwellingor structure to be constructed and evaluated.

The term “characterization” can also include identifying if theelectrical power distribution system has any deficiencies that areshock-hazards, fire-hazards, code violations, or other defects that arenot easily determined in systems that cannot be easily accessed orvisually inspected.

One outcome of the characterization process would include adetermination of whether the system can perform its intended functionsafely and in the manner it was designed. Another outcome would includea determination of whether there are any design deficiencies, or if theblueprint contains code violations.

For the purposes of discussion here, the term “condition” means thefollowing: A system in “good” condition can supply the rated loads tothe circuits being tested without presenting a fire danger. Such asystem can be considered safe to use in the method for which it israted. A system in “fair” condition can supply the rated loads, butmight have code violations or wiring deficiencies that need attention.Such a system might need repair, but can still be used without near-termhazard. A system in “poor” condition has one or more faults that areshock or fire hazards, or prohibit the rated load from being deliveredto one or more outlets or test points. A system in “poor” conditionwould normally not be used until it is repaired. It should bede-energized.

For the purposes of discussion here, the term “fault” includes anycondition that presents a potential health, shock, or fire hazard orviolation of generally accepted safe construction or wiring practices. Afault may include improper modifications to, or be the result ofdeterioration to, a properly designed system. Other faults may be theresult of changes to design, codes, and construction practices. Systemsdesigned in a given year according to generally accepted safe practicesmay, even in the absence of significant deterioration, have faults ofdesign, wiring, or construction that are identified in subsequent yearsas a result of changing practices or codes.

An example of a fault that is a potential fire hazard is the use ofwiring that does not have the ampacity to supply the load rating for afuse or circuit-breaker in its path. This is a fault of design orconstruction.

Another example of a fault includes sharing the main branch circuit fora bathroom in a business or residence as the supply for other rooms.Another example is omitting ground-fault protection in the main branchcircuit for a kitchen or bathroom. These are examples of faults that maybe the result of changes in generally accepted codes, since residencesbuilt prior to certain years were not required to have ground faultprotection.

Another example of a fault includes a point of high resistance in ajunction box because of deterioration of a junction contained in thebox. Another example is a point or area of high resistance in aninaccessible location that is the result of action by vermin or weather.These two examples are faults due to deterioration of what was formerlya safe electrical system. Points of high resistance are widelyrecognized as fire hazards. For embodiments, characterizing the powerdistribution system includes determining if there is a fault at onelocation or more than one location.

Another example of a fault includes excessive temperature, which mayresult from improper bundling or routing of wiring or cables or the useof wiring that cannot supply sufficient load. Such a fault would notnecessarily be obvious by inspection since electrical codes can onlysupply guidelines for routing and cannot cover all circumstances.

As described, the test signals can be applied to at least one test pointand a plurality of responses to the test signal observed. A test signalcan be active or passive.

A passive test signal has the property that it is a resistive orreactive load. Generally, a passive test signal would be applied tocircuits that are energized by some other means such as through itsnormal connection to the service panel. One example of a response signalthat is measured during the application of a passive test signal couldbe any change in voltage of the already-energized circuit as the passivetest signal is applied.

An active test signal has the property that it supplies its own sourceof power, for example, an injected current. An active test signal hasthe advantage that it may be used in circuits that are not energized.

The application of a test signal can include application of passiveresistive or reactive load or active injection of voltage or currentsignal. By applying a test signal in the form of a known calibrated loadto an outlet of known voltage, the electrical current can be measured todetermine if the branch circuit conductors connected to the outlet areable to supply the necessary power to the circuit. The injection of avoltage or current test signal is sometimes used to look for breakagesin electrical networks, where the reflection of the signal from thisbreakage is used to determine the approximate location and severity ofthe break.

A “response-signal” at a test point may constitute any of voltage,current, temperature, resistance, conductance, impedance, inductance, orcapacitance, or similar physical attribute associated with an electricalsystem or network. The instrument measuring the response signal shouldnot influence the circuit appreciably by drawing significant current orbeing a significant load. It is to be understood that a response signalmay be measured with or without application of a test signal generatedby a T/R unit. It is often the case that the difference in the responsesignal before application and during application of a test signal by aT/R unit is of significance, especially on a power distribution systemthat is live (is powered by external means). An example of a responsesignal that can be made without a test signal generated by a T/R unitincludes voltage measurements between contacts at a test point in a livecircuit. In this case, the line voltage already supplied in the livecircuit acts as a test signal not supplied by a T/R unit. Similarly, aplurality of T/R units may make measurements of voltages at a pluralityof test points with no test signal generated by a T/R unit. Suchmeasurements of response signals without having the T/R unit generatetest signals establish a “baseline” which is used in thecharacterization of the electrical circuit.

After the baseline is established, a T/R unit may supply a resistiveload at a test point as an example of a T/R unit generated test signal.During the application of this load, a plurality of T/R units may makemeasurements of the response signals. The differences in responsesignals (in this example, voltage differences between baseline andapplication of the resistive load) may be used to characterize theelectrical power distribution system.

If the power distribution system is not live at the time of testing, aT/R unit may apply a test signal that supplies voltage to the circuit sothat all T/R units may establish a baseline. Such a test signal used forestablishing a baseline is called a “baseline signal.” If the circuit islive at the time of testing, the signal already present may be calledthe “baseline signal”. The response measured by a T/R unit to a baselinesignal is called a “baseline measurement.” Hence, a baseline measurementmay be made with or without a T/R unit supplying the baseline signal.

FIGS. 2A and 2B show exemplary configurations of electrical distributionsystems that can be characterized using the described embodiments. Thetwo figures show a service panel and two test points (in this example,power outlets) having configurations that differ in the way that thepower outlets are electrically connected to the service panel. Bothconfigurations are generally allowable according to commonly-acceptedelectrical codes and are functionally equivalent to the user connectingto the system. However, to a person characterizing and testing thesystem, they are different. But all that is generally accessible are thetwo outlets and the service panel. It is not generally obvious whichconfiguration applies since the wiring is not necessarily accessible forobservation.

It is assumed that a characterization is required, and part of thischaracterization is to determine whether the model of FIG. 2A or 2Bapplies, and if there are one or more faults in the distribution system.

It is readily apparent that two outlets may be connected in many otherways as part of a larger power distribution system. To limit the scopeof the discussion, only the possible configurations in FIGS. 2A and 2Bare considered.

The resistive paths R1-R9 model the presence or absence of wires. Lowresistance models a wire that is present and in good condition, and highresistance models a wire that is absent or in poor condition. Thedifference in the two figures lies in which wires are present. As shown,the resistive paths R7, R8, R9 of FIG. 2A are high-resistance,indicating absence of those paths, while R4, R5, R6 are high-resistancein FIG. 2B.

The resistive paths RH and RG represent resistance between theElectrical Distribution Box (280) and the external electrical servicesupplying the distribution box.

The described embodiments can be used to characterize the powerdistribution system. This characterization is now described in moredetail. It is assumed that the circuit is live at the time of testing.

As part of the characterization, the T/R units 1, 2, and 3 establish abaseline of voltage measurements at the three test points before theapplication of any T/R-generated test signal. Application of testsignals by one or more of the T/R units 210, 220, 230 and measurementsof responses at each of the T/R units 210, 220, 230 can then deducewhere the high-resistance (and low-resistance) paths are located. Theresponse signals of the electrical distribution system of FIG. 2A differfrom the response signals of the electrical distribution system of FIG.2B. A detailed description follows.

It is important to note that even if only one T/R unit is applying atest signal, it is the measuring of a plurality of response signals witha plurality of T/R units that enables the controller to ascertain whichconfiguration applies.

In one stage of the characterization, T/R units 1, 2, and 3 are allinstructed to measure their respective H-N voltage as a response signal,using the fact that the circuit is live and therefore has a test signalreadily available. This establishes the baseline.

In another stage of the characterization, T/R unit 1 is instructed bythe controller to apply a test signal that is a known resistive loadbetween H1 and N1, at which points T/R units 1, 2, and 3, are allinstructed to measure their respective response-signals that includesthe voltages between their respective H and N contacts.

In the case of the power distribution system depicted in FIG. 2A, T/Runit 2 shows that the H2-N2 voltage is substantially the same as the H-Nvoltage measured by T/R unit 3. Furthermore, the H1-N1 voltage is lowerthan H2-N2 (or H-N). The amount that it is lower is determined by R1 andR2 and the size of the applied resistive load and current that is drawn.

However, this same test procedure applied to FIG. 2B results in the T/Runit 2 showing substantially the same H2-N2 voltage as H1-N1, and bothare lower than the H-N voltage measured by T/R unit 3.

In another stage of the characterization, a resistive load from H2 to N2at T/R unit 2 is applied, and H-N voltage measurements taken at allthree test units. Further information about the configuration and actualresistance values are thereby obtained, depending on the relative valuesof H-N, H1-N1, and H2-N2 voltage. It should be noted that the order ofwhere test signals are applied is generally not unique, nor are thevariety of response-signals that may be measured. It is, however,important that response signals are measured at a plurality of testpoints in response to each test signal.

At the conclusion of the test procedure, the response signals measuredby all T/R units are collated by a controller. The controller then maycharacterize the system, decide the configuration and the presence orabsence of any faults.

Some exemplary calculations are:

-   -   1) A baseline measurement of response signals is made by all        three T/R units before any test signals are applied. In this        case it is assumed that there is an active electrical        distribution voltage present and that the T/R units may utilize        this voltage during its characterization. The voltages should        obey

V _(HN) ^((B)) =V _(H1N1) ^((B)) =V _(H2N2) ^((B))

where the superscript “(B)” means that it is a baseline measurement, andthe subscript “HN” represents that T/R unit 3 is measuring the voltagebetween “H” and “N” (or Hot and Neutral), and similarly, for H1N1 andH2N2. Any significant deviation from these values indicates that thereare wiring problems or unanticipated loads active on the circuit.

-   -   2) Then, T/R unit I applies a resistive load R_(L) between H1        and N1. The following equations apply:

${R_{H} + R_{G}} = \frac{V_{HN}^{(B)} - V_{HN}^{(1)}}{I_{H\; 1N\; 1}^{(1)}}$

where the superscript “(1)” indicates that this is the firstnon-baseline test/response measurement being made. It is assumed thatvoltage (V) and current (I) response signal measurements are availableat the T/R units. Large values for R_(H)+R_(G) indicate a fault betweenthe electrical distribution box and the external service. Otherequations that apply include:

$V_{H\; 2N\; 2}^{(1)} = {V_{HN}^{(1)} - {V_{{HH}\; 1}^{(1)}\frac{R_{4}}{R_{4} + R_{7}}} - {V_{N\; 1N}^{(1)}\frac{R_{5}}{R_{5} + R_{8}}}}$and$V_{H\; 1N\; 1}^{(1)} = \frac{R_{L}V_{HN}^{(1)}}{R_{L} + \frac{R_{1}( {R_{4} + R_{7}} )}{R_{1} + R_{4} + R_{7}} + \frac{R_{2}( {R_{5} + R_{8}} )}{R_{2} + R_{5} + R_{8}}}$

It is to be noted that V_(HH1) and V_(N1N) may not be measureable by aT/R unit since they represent voltage measurements between more than onetest point.

-   -   3) Then, T/R unit 2 applies a resistive load R_(L) between H2        and N2 and a another set of equations may be derived:

$V_{H\; 1N\; 1}^{(2)} = {V_{HN}^{(2)} - {V_{{HH}\; 2}^{(2)}\frac{R_{1}}{R_{1} + R_{7}}} - {V_{N\; 2N}^{(2)}\frac{R_{2}}{R_{2} + R_{8}}}}$and$V_{H\; 2N\; 2}^{(2)} = \frac{R_{L}V_{HN}^{(2)}}{R_{L} + \frac{R_{4}( {R_{1} + R_{7}} )}{R_{1} + R_{4} + R_{7}} + \frac{R_{5}( {R_{2} + R_{8}} )}{R_{2} + R_{5} + R_{8}}}$

wherein the superscript “(2)” indicates that this is the secondnon-baseline test/response measurement.

-   -   4) The central controller is informed of the measurements V        _(HN), V_(H1N1), V_(H2N2), (both baseline and non-baseline) and        characterizes the electrical distribution system by computing        R1-R9 and RH and RG to the extent possible. Some of the        computations it may make include, for example, assuming that the        ratios

$\frac{R_{4}}{R_{4} + R_{7}} = {\frac{R_{5}}{R_{5} + R_{8}} = \alpha}$

are equal (calling this ratio a) and then obtaining

$\alpha = \frac{V_{HN}^{(1)} - V_{H\; 2N\; 2}^{(1)}}{V_{HN}^{(1)} - V_{H\; 1N\; 1}^{(1)}}$

The controller generally expects α to be either 0 or 1, depending onwhether R7 is large (open circuit in FIG. 2A) or R4 is large (opencircuit in FIG. 2B). Any value other than 0 or 1 may indicate a fault.

-   -   5) There are many similar calculations with the remaining        equations that characterize the electrical distribution system.        Continuing in this way, the controller identifies whether FIG.        2A or 2B applies, and computes remaining resistance values.

FIG. 3 is a flow chart that includes some of the steps described aboveas a method of characterizing an electrical power distribution system. Afirst step 310 includes connecting a plurality of T/R units to the testpoints of the electrical distribution system. A second step 320 includesmeasuring a plurality of response signals at a plurality of test pointsto establish a baseline. A third step 330 includes applying at least onetest signal to at least one test point of the system. A fourth step 340includes measuring a plurality of response signals at a plurality oftest points, wherein the plurality of response signals are generated inresponse to the at least one test signal. A fifth step 350 includescharacterizing the system based on the plurality of response signals.

An embodiment of a test point includes at least one electrical contact.An embodiment includes a test signal being applied between pairs ofelectrical contacts at a test point. For an embodiment, the test signalincludes at least one of a resistive or reactive load or static injectedcurrent. For another embodiment, the test signal includes at least oneof a time-varying resistive or reactive load, or a time-varying injectedcurrent.

For some embodiments, characterizing the electrical power distributionsystem based on the plurality of response signals includes deducingelectrical properties of the individual branches of the electrical powerdistribution system. For other embodiments, characterizing theelectrical power distribution system based on the plurality of responsesignals includes locating at least one fault within the system.

As previously described, baseline measurements can be made beforeapplication of test signals. That is, a baseline measurement at one ormore test points can be established before applying the at least onetest signal. The baseline measurement can be established by measuring asignal response without applying any external signals, or the baselinemeasurement can be established by applying a baseline signal at one ormore test points.

Embodiments include one or more measurements being observed fortime-variations to indicate time-varying effects. An example of atime-varying effect is due to heating that accompanies the flow ofcurrent through localized high resistance. Current drawn through adefective or corroded junction of wires having a local high-resistancecontact, for example, may cause the junction to heat excessively. Thisheat could manifest itself as a change in the current drawn through afixed load over time.

Embodiments include application of at least one test signal and themeasurement of a plurality of response signals being coordinatedaccording to a schedule. One embodiment of the schedule includessubstantially simultaneous measurements of each of the plurality ofresponse signals. That is, more information can be obtained by asimultaneous measurement than by both measurements made separately. Forexample, separate measurements at two locations might indicate a problemat each test point individually, but cannot tell whether these twoproblems are distinct or actually originate from one common problem.Only by simultaneous measurements can important details such as these bedetermined. The term “simultaneous measurements” means measurementstaken substantially at the same time or within the time-constant of thesystem being tested. It is well-known to practitioners in the art thatcurrent digital systems often make measurements by sampling usinganalog-to-digital converters. Such sampling is often governed byhigh-frequency clocks. Sampling by two different devices, using theirrespective clocks, may therefore not be precisely at the same time, butconsidered simultaneous nevertheless for the purposes of the time-scalesof the system being tested.

Other embodiments include applying one or more test signalssimultaneously at distinct test points. The intention being thatinformation can be obtained by the simultaneous application of multiplesignals that cannot be obtained by the application of just one signal,even if this one signal is applied at different non-overlapping times atthose same test points. In a similar fashion, information can beobtained by the simultaneous measurement at multiple test points thatcannot be obtained by measuring at just one test point.

The previously mentioned scheduled can be determined by a centralcontroller initiating the application of test signals and coordinatingthe measurement of the plurality of response signals. Further,embodiments include the central controller receiving the responsesignals and performing the characterization of the electrical powerdistribution system based on the plurality of response signals.

For embodiments, characterizing the electrical power distribution systembased on the plurality of response signals includes generating ablue-print of the system. Embodiments include the blue-print of theelectrical power distribution system being obtained, in part, bydeducing the resistances of the individual branch circuits of thesystem. The “electrical blueprint” of the electrical distribution systemcan be constructed noninvasively. Such a blueprint can provideinformation about the various circuits contained within the structure asthey originate from a centralized feed, pass through somecurrent-limiting device such as a circuit breaker or fuse, and then aredistributed throughout the structure. The blueprint provides informationon which circuits are directly connected to each other and which arenot. While an electrical blueprint is sometimes available when abuilding is new, such blueprints become obsolete as soon as the firstmodification to the structure is made. Being able to make such ablueprint on-demand, noninvasively, and without prior knowledge of theexisting wiring, would be very desirable. The described embodiment fordetermining the condition of the electrical distribution system iseconomical to implement and can be readily automated. The controller mayinstruct the T/R units which test signals to apply and which responsesignals to measure.

FIG. 4 shows an example of a test/response (T/R) unit 400. The unit 400includes a controller 430. The controller 430 controls a test signalgeneration unit 410 that applies a passive or active signal to one ormore test points. A response measurement unit 420 measures responsesignals at one or more test points. A communications interface 440provides the unit 400 with the ability to communicate with other T/Runits or another control unit. A display unit 450 can provideinformation to a user of the unit 400.

The unit 400 can characterize an electrical system that the test pointshown in FIG. 4 is connected to. The unit 400 can operate alone, or inconjunction with at least one other T/R unit. The unit 400 (andoptionally other units as well) apply at least one test signal to atleast one test point of the electrical distribution system. The unit(s)measure a plurality of response signals at a plurality of test points,wherein the plurality of response signals are generated in response tothe at least one test signal. The unit(s) can characterize the systembased on the plurality of response signals.

FIG. 5 shows an example of multiple test/response (T/R) units 510, 520,530 and a central controller 540 for characterizing an electricaldistribution system. The T/R units 510, 520, 530 are connected to testpoints of the electrical power distribution system as previouslydescribed. Additionally, the T/R units 510, 520, 530 are connected tothe central controller through communications channels 550. Embodimentsinclude the controller managing the application of test signals by theT/R units 510, 520, 530, and characterizing the electrical powerdistribution system based on response signals measured by the T/R units510, 520, 530.

The communications channel 550 can utilize any number of availablecommunications link technologies. A conceptually straightforwardcommunication channel consists of a wire which links all T/R unitstogether and to the controllers(s). Having a common wire at each T/Runit would facilitate the measurement process by establishing auniversal reference potential. However the deployment of a common wirecould add to operational difficulties. Alternatively the electricaldistribution system itself could constitute a communications channelusing known principles and hardware. However difficulties could beexperienced where a circuit is electrically isolated from the rest ofthe electrical distribution system, either because of an open switch, orbecause the circuit has been abandoned and is not energized. Stillanother alternative is a wireless communications channel using, forexample, unlicensed spectrum. This requires a T/R unit and processor tocontain a wireless transceiver. Known technologies such as Wi-Fi couldbe used.

FIG. 6 is a flow chart that includes steps of another example of amethod of characterizing an electrical power distribution system. A step610 includes applying a plurality of test signals (as opposed toapplying a single test signal) to a plurality of test points of thesystem. A subsequent step 620 includes measuring a response signal atone or more test points, wherein the response signals are generated inresponse to the plurality of test signals. A subsequent step 630includes characterizing the system based on the at least one responsesignal. As previously described, embodiments include characterizing theelectrical power distribution system based on the at-least one responsesignal, including locating at least one fault within the system. For aspecific embodiment, locating at least one fault within the electricalpower distribution system includes locating high electrical resistancein the system.

Although specific embodiments have been described and illustrated, theembodiments are not to be limited to the specific forms or arrangementsof parts so described and illustrated. The embodiments are limited onlyby the appended claims.

What is claimed:
 1. A method of characterizing an electrical powerdistribution system, comprising: applying at least one test signal to atleast one test point of the system; measuring a plurality of responsesignals at a plurality of test points, wherein the plurality of responsesignals are generated in response to the at least one test signal; andcharacterizing the system based on the plurality of response signals. 2.The method of claim 1, wherein each of the test points comprises atleast one electrical contact.
 3. The method of claim 1, furthercomprising establishing a baseline measurement at one or more testpoints before applying the at least one test signal.
 4. The method ofclaim 3, wherein establishing the baseline measurement comprisesmeasuring a signal response without applying any external signals. 5.The method of claim 3, wherein establishing the baseline measurementcomprises applying a baseline signal at one or more test points.
 6. Themethod of claim 1, wherein characterizing the electrical powerdistribution system based on the plurality of response signals includesdeducing electrical properties of the individual branches of theelectrical power distribution system.
 7. The method of claim 1, whereincharacterizing the electrical power distribution system based on theplurality of response signals comprises locating at least one faultwithin the system.
 8. The method of claim 1, wherein one or moremeasurements is observed for time-variations to indicate time-varyingeffects.
 9. The method of claim 1, wherein a test signal is appliedbetween pairs of electrical contacts at a test point.
 10. The method ofclaim 1, wherein a test signal includes at least one of a static load orstatic injected current.
 11. The method of claim 1, wherein a testsignal includes at least one of a time-varying resistive or reactiveload, or a time-varying injected current.
 12. The method of claim 1,wherein the application of at least one test signal and the measurementof a plurality of response signals is coordinated according to aschedule.
 13. The method of claim 12, wherein the schedule comprisessubstantially simultaneous measurements of each of the plurality ofresponse signals.
 14. The method of claim 12, wherein the schedule isdetermined by a central controller initiating the application of testsignals and coordinating the measurement of the plurality of responsesignals.
 15. The method of claim 14, further comprising the centralcontroller receiving the response signals and performing thecharacterization of the electrical power distribution system based onthe plurality of response signals.
 16. The method of claim 1, whereincharacterizing the electrical power distribution system based on theplurality of response signals comprises generating a blue-print of thesystem.
 17. The method of claim 16, wherein the blue-print of theelectrical power distribution system is obtained, in part, by deducingthe resistances of the individual branch circuits of the system.
 18. Amethod of characterizing an electrical power distribution system,comprising: applying a plurality of test signals to a plurality of testpoints of the system; measuring a response signal at one or more testpoints, wherein the response signals are generated in response to theplurality of test signals; and characterizing the system based on the atleast one response signal.
 19. The method of claim 18, whereincharacterizing the electrical power distribution system based on theat-least one response signal includes locating at least one fault withinthe system.
 20. The method of claim 19, wherein locating at least onefault within the electrical power distribution system includes locatinghigh electrical resistance in the system.
 21. A system forcharacterizing an electrical power distribution system, comprising: aplurality of test/response units attached to a plurality of test points,said units configured to, at least one of, generate test signals ormeasure response signals at the plurality of test points; at least onecontroller coordinating application of test signals and characterizingthe electrical power distribution system based on the response signals;a communications link between the test/response units allowing thetest/response units to communicate with the at least one controller. 22.The method of claim 21, wherein the at least one controller determines aschedule for application of the test signals and measurement of responsesignals.
 23. The method of claim 21, wherein the at least one controlleris a central controller.
 24. The method of claim 21, wherein the atleast one controller is a distributed controller.
 25. The method ofclaim 21, wherein characterizing the electrical power distributionsystem based on the response signals comprises locating at least onefault within the system.
 26. The method of claim 21, wherein theresponse signals are used to deduce , electrical properties ofindividual branch conductors of the electrical power distributionsystem.
 27. A test/response unit that is connectable to an electricalpower distribution system through a test point, the unit operative to:apply at least one test signal to the test point; measure at least oneresponse signal at the test point, wherein the response signal isgenerated in response to the test signal; receive instructions onapplication of the test signal from, or to transmit results of the atleast one measured response signal to another test/response unit orcoordinating controller.
 28. A test/response unit that is connectable toan electrical power distribution system through a test point, the unitoperative to: apply at least one test signal to the test point; measureat least one response signal at the test point, wherein the responsesignal is generated in response to a test signal applied at another testpoint of the electrical power distribution system; receive instructionson application of the test signal from, or transmit the results of itsmeasured response signal to, another test/response unit or coordinatingcontroller.